Embossing is the process of creating a three-dimensional image or design in paper and other ductile materials. It is typically accomplished with a combination of heat and pressure on the paper. This is achieved by using a metal die (female) usually made of brass or stainless steel and a counter die (male) that fit together and actually squeeze the fibers of the paper. This pressure and a combination of heat actuated “irons” raise the level of the image higher than the substrate and make it smooth. This can be performed on dry or wet papers. The process works because the paper is malleable; it will embrace and retain an image of whatever object is pressed against it.
A paperboard is a sheet of fibrous web material having a grammage higher than 125 grams per square meter, by comparison with papers which have a grammage below 125 grams per square meter. A paperboard is embossed to increase its volume and, simultaneously reduce the quantity of raw material necessary to manufacture the paperboard for a given thickness. It therefore increases the specific volume (or bulk).
However, dry embossing crushes the fibers of the paperboard and therefore weakens substantially the resulting paperboard. Dry embossing delaminate boards made of multiple plies.
Peak to peak embossing perforates the pulp-based substrate and therefore alters substantially its mechanical properties.
Techniques other than embossing to increase the volume of the paperboard are currently used but all yield unacceptable results with respect to volume of the paperboard, quantity of fibers used and strength of the resulting paperboard. Such techniques are, for example, reducing the wet pressing, reducing the refining, adding sawdust in the wet mat, adding mechanical pulp and chemicals.